Transmission logic parity circuit

ABSTRACT

An FET transmission logic parity circuit is disclosed which determines the odd or even status of register bits using zero DC current transmission logic. The circuit has a first two FET devices which propagate the state of the preceding odd or even nodes and the corresponding register bit is logically a zero. A second pair of FET devices switch the state of the odd or even nodes when the corresponding register bit is logically a one. In this manner, the output nodes are statically conditioned to either a first potential or a second potential, depending upon the register bit states and no DC current flows between the first and second potential.

FIELD OF THE INVENTION

The invention disclosed broadly relates to semiconductor circuits and more particularly relates to an improved FET parity generation circuit.

BACKGROUND OF THE INVENTION

Parity generation pertains to the use of a self-checking code employing binary digits in which the total number of ones (or zeros) in each permissible code expression is always even or always odd. A check may then be made for either even parity or odd parity to determine whether errors have occurred in the binary digit. The parity bit is a binary number appended to the array of bits to make the sum of all the bits always odd or always even.

A variety of parity generation and checking circuits have been described in the prior art. Each improvement attempts to increase the speed and reduce the size of the circuit for generating a parity bit from a multiple digit binary number. A typical approach is shown in U.S. Pat. No. 4,224,680 which discloses a parity checker which includes a ripple-carry type counter where the parity bit is produced by a single network of NAND gates connected in series from high order to low order counter bits. One significant problem with such prior art parity generation and checking circuits is that as they become progressively smaller when embodied on an integrated circuit chip, the power dissipated by the circuit per unit area tends to increase, thereby limiting both the size and the speed of the resultant parity generation circuit.

OBJECT OF THE INVENTION

It is therefore an object of the invention to provide an improved parity generation circuit.

It is therefore another object of the invention to provide a parity generation circuit which dissipates a minimum quantity of power.

It is still a further object of the invention to provide an improved parity generation circuit having a simple topology and small layout area.

It is yet a further object of the invention to provide an improved parity generation circuit which is capable of integration on an integrated circuit chip in a small layout area and yet dissipates a relatively small quantity of power per unit area.

SUMMARY OF THE INVENTION

These and other objects, features and advantages of the invention are achieved by the transmission logic parity circuit disclosed herein. An FET transmission logic parity circuit is disclosed which determines the odd or even status of register bits using zero DC current transmission logic. The circuit has a first two FET devices which propagate the state of the preceding odd or even nodes and the corresponding register bit is logically a zero. A second pair of FET devices switch the state of the odd or even nodes when the corresponding register bit is logically a one. In this manner, the output nodes are statically conditioned to either a first potential or a second potential, depending upon the register bit states and no DC current flows between the first and second potentials.

DESCRIPTION OF THE FIGURES

These and other objects, features and advantages of the invention will be more fully appreciated with reference to the accompanying figures.

FIG. 1 illustrates a schematic circuit diagram of the transmission logic parity circuit invention.

DISCUSSION OF THE PREFERRED EMBODIMENT

An FET transmission logic parity circuit is disclosed which determines the odd or even status of register bits using zero DC current transmission logic. The circuit has a first two FET devices which propagate the state of the preceding odd or even nodes and the corresponding register bit is logically a zero. A second pair of FET devices switch the state of the odd or even nodes when the corresponding register bit is logically a one. In this manner, the output nodes are statically conditioned to either a first potential or a second potential, depending upon the register bit states and no DC current flows between the first and second potentials.

The parity circuit is shown in FIG. 1, for determining whether an odd or even number of binary bits having a value of one, are present, at an n-bit plurality of binary operand bit inputs. The circuit includes n-stages of sequentially connected steering cells, each cell including a true-value binary bit operand input A_(n-1) and a complementary-value binary bit operand input A_(n-1) for one of the plurality of operand bit inputs, a first E_(n) and a second O_(n) indicating potential input terminals and a first E_(n-1) and a second O_(n-1) indicating potential output terminals.

The first indicating potential input terminal of an i-th cell is connected to the first indicating potential output terminal of the next preceding i+1th cell and the second indicating potential input terminal of the i-th cell is connected to the second indicating potential output terminal of the next preceding i+1th cell.

A first FET device T₁ in each cell has its drain connected to the first indicating potential input terminal thereof, its source connected to the first indicating potential output terminal thereof, and its gate connected to the complementary-value binary bit operand input thereof.

A second FET device T₂ in each cell has its drain connected to the second indicating potential input terminal thereof, its source connected to the first indicating potential output terminal thereof, and its gate connected to the true-value binary bit operand input thereof.

A third FET device T₃ in each cell has its drain connected to the first indicating potential input terminal thereof, its source connected to the second indicating potential output terminal thereof, and its gate connected to the true-value binary bit operand input thereof.

A fourth FET device T₄ in each cell has its drain connected to the second indicating potential input terminal thereof, its source connected to the second indicating potential output terminal thereof, and its gate connected to the complementary-value binary bit operand input thereof.

The first FET device T₁ in one of the cells of interest forms a conductive path between the first indicating potential input terminal E_(n) and the first indicating potential output terminal E_(n-1) and the fourth FET device T₄ in the cell forming a conductive path between the second indicating potential input terminal O_(n) and the second indicating potential output terminal O_(n-1) when the complementary-value binary bit operand input A_(n-1) in the cell is active.

The third FET device T₃ in the cell of interest forms a conductive path between the first indicating potential input terminal E_(n) and the second indicating potential output terminal O_(n-1) and the second FET device T₂ in the cell forming a conductive path between the second indicating potential input terminal O_(n) and the first indicating potential output terminal E_(n-1) when the true-value binary bit operand input A_(n-1) in the cell is active.

The first indicating potential input terminal in a first one of the cells in the sequence has a first potential V_(dd) applied to it corresponding to a binary one bit value and the second indicating potential input terminal in the first cell has a second potential Gnd applied to it corresponding to a binary zero bit value.

The second indicating potential output terminal O₀ in a last one of the cells in the sequence outputs a signal corresponding to the first potential V_(dd) in response to an odd number of the cells having their respective true-value binary bit operand input active indicating an odd parity and the second indicating potential output terminal O₀ in the last cell outputs a signal corresponding to the second potential Gnd in response to an even number of the cells having their respective true-value binary bit operand input active indicating an even parity.

The circuit shown in FIG. 1 is provided with an odd output comprising the inverter T₅ and T₆ and an even output provided by the inverter T₇ and T₈. The node O₀ is connected to the gate of the depletion mode active load device T₆ and is also connected to the gate of the enhancement mode active device T₇. The node E₀ is connected to the gate of the enhancement mode active FET device T₅ and the depletion mode active load FET device T₈. For N channel FET devices having V_(dd) as a positive potential with respect to ground, when there is an even parity (an even number of binary ones in a word having an even number of binary digits), node O₀ will be at ground and node E₀ will be at a positive potential, thereby making the odd output of the inverter T₅ and T₆ at ground potential and the even output of the inverter T₇ and T₈ at positive potential. Alternately, when there is an odd parity (an odd number of binary ones for a word having an even number of binary digits), the node O₀ is at a positive potential and the node E₀ is at ground potential, thereby placing the odd output of the inverter T₅ and T₆ at a positive potential and the even output of the inverter T₇ and T₈ at ground potential

OPERATION OF THE INVENTION

Reference to FIG. 1 will show that the successive stages of the parity circuit are identical and in order to follow the operation of the circuit, the FET devices in each respective stage have been identified with the same subscript as the corresponding devices in the other stages and with a superscript prime to distinguish devices in one stage from those in another. The operation of the circuit will be illustrated for a binary word having four binary digits, and thus the four stages illustrated in FIG. 1 will be considered as the full complement of stages for a four-bit parity circuit.

Consider first the generation of a parity bit for the even parity four digit word 0011. For an N channel FET circuit, the positive potential V_(dd) will be considered a binary one and ground potential will be considered a binary zero. For this example, the binary word will provide the values A_(n) =0, A_(n-1) =0, A_(n-2) =1, and A₀ =1. Correspondingly, A_(n) =1, A_(n-1) =1, A_(n-2) =0, and A₀ =0.

For the topmost or first stage, since A_(n) =0, ground potential is applied to the gates of transistors T₂ and T₃ keeping them off and since A_(n) =1, +V_(dd) potential will be applied to the gates of transistors T₁ and T₄ turning them on. Since the potential at the drain of the enhancement mode device T₁, which is +V_(dd), equals the potential on the gate of the transistor T₁, the potential at the source of the transistor T₁ will be V_(dd) minus V_(th), that is the potential at the source of T₁ is equal to the potential at the drain of T₁ less the threshold voltage of the enhancement mode FET device T₁. The potential at the drain of T₄ is ground potential which is less than the potential at the gate of T₄ which is V_(dd). Thus the ground potential at the drain of T₄ is transferred undiminished to the source of T₄.

At the second topmost stage of the circuit in FIG. 1, the potential at the node E_(n) equals V_(dd) minus V_(th) and the potential at the node O_(n) equals ground potential, as mentioned above. Since A_(n-1) =0, ground potential is applied to the gates of the transistors T₂ ' and T₃ ', maintaining them in an off state. Correspondingly, since A_(n-1) is a binary one, a +V_(dd) potential is applied to the gates of transistors T₁ ' and T₄ ', maintaining them in an on state. Since the potential at the drain of the transistor T₁ ' is V_(dd) minus V_(th) which is less than the gate potential at T₁ ' of V_(dd), the potential at the drain of the transistor T₁ ' is transferred undiminished to its source so that the node E_(n-1) will be at the potential of V_(dd) minus V_(th). It should be noticed at this point that the diminution of the potential at the drain of T₁ in the first stage by the threshold voltage of T₁, occurs only once for the entire sequence of stages in the parity circuit of FIG. 1. Since T₄ ' is on, the ground potential at the node O_(n) will be transferred undiminished to the node O_(n-1).

At the third topmost stage in FIG. 1, the node E_(n-1) equals V_(dd) minus V_(th) and the node O_(n-1) equals ground potential. Since A_(n-2) has a binary value of one, a +V_(dd) potential is applied to the gates of transistors T₂ " and T₃ ", maintaining both transistors in the on state. Correspondingly, since A_(n-2) has a binary zero value, ground potential is applied to the gates of the transistors T₁ " and T₄ ", thereby maintaining these transistors in an off state. The ground potential at the node O_(n-1) is transferred undiminished through T₂ " to its source at the node E_(n-2). The potential V_(dd) minus V_(th) at the node E_(n-1) is transferred through the device T₃ " to the node O_(n-2). It should be noted here that the symmetry of the positive and ground potentials on the E and O nodes has been changed at the third stage because A_(n-2) is a binary one.

At the fourth or bottommost stage in FIG. 1, the node E_(n-2) is at ground potential and the node O_(n-2) is at a potential of V_(dd) minus V_(th). Since A₀ has a binary one value, a +V_(dd) potential is applied to the gates of transistors T₂ '" and T₃ '" maintaining these devices in an on state. Correspondingly, since A₀ has a binary zero value, ground potential is applied to the gates of the transistors T₁ '" and T₄ '", maintaining these two devices in their off state. Thus, the ground potential at the node E_(n-2) is transferred undiminished through the transistor device T₃ '" to node O₀. And the potential V_(dd) minus V_(th) at the node O_(n-2) is transferred undiminished through the transistor device T₂ '" to the node E₀. Once again, it should be noticed that the symmetry of the positive potential and the ground potential for the E and O nodes has been reversed because A₀ is a binary one value.

All of the FET devices in FIG. 1 are enhancement mode devices except for the two depletion mode devices T₆ and T₈. When ground potential is applied at the node O₀ to the gate of the active depletion mode device T₆, it is turned almost completely off, and when the positive potential V_(dd) minus V_(th) at node E₀ is applied to the gate of enhancement mode transistor T₅ turning it on, the odd output of the inverter T₅ and T₆ is at ground potential corresponding to a binary zero value. One can interpret this output as indicating that the parity is not odd.

Conversely, the ground potential of the node O₀ is applied to the gate of the enhancement mode FET device T₇, turning it off, and the positive potential V_(dd) minus V_(th) is applied to the gate of the depletion mode active load device T₈, turning it fully on. Since a fully on depletion mode FET device will transfer its drain potential undiminished to its source, the even output node of the inverter T₇ and T₈ will have the potential of V_(dd) which corresponds to a binary one. The even output having a value equal to a binary one can be interpreted as the four digit binary word input to the circuit having an even number of binary ones or an even parity.

A second example will now be given of an odd parity four digit binary word being processed by the circuit of FIG. 1. An example odd parity four digit binary word of 0100 will be considered. A_(n) will equal 0, A_(n-1) will equal 1, A_(n-2) will equal 0, and A₀ will equal 0. Correspondingly, A_(n) will equal 1, A_(n-1) will equal 0, A_(n-2) will equal 1, and A₀ will equal 1. Once again, N channel FET devices will be considered in this example so that V_(dd) will be a positive potential with respect to ground.

In the first or topmost stage of FIG. 1, since A_(n) has a binary value of zero, ground potential is applied to the gates of transistors T₂ and T₃, thereby maintaining them in an off state. Correspondingly, since A_(n) has a binary one value, the positive potential V_(dd) will be applied to the gates of transistors T₁ and T₄, thereby maintaining them in an on state. The potential V_(dd) at the drain of the transistor T₁ will be transferred to the source of transistor T₁, diminished by the threshold voltage V_(th) of transistor T₁, in a manner similar to that described above. Correspondingly, ground potential at the drain of transistor T₄ will be transferred undiminished to its source. Thus, the node E_(n) will have a potential V_(dd) minus V_(th) and the node O_(n) will be at ground potential.

Since A_(n-1) has a binary value of one, a positive potential of V_(dd) will be applied to the gates of transistors T₂ ' and T₃ ', maintaining these two devices in their on state. Correspondingly, since A_(n-1) has a binary zero value, ground potential will be applied to the gates of transistor devices T₁ ' and T₄ ', maintaining these two devices in their off state. Thus the ground potential at the node O_(n) will be transferred undiminished through the transistor T₂ ' to the node E_(n-1). The positive potential V_(dd) minus V_(th) at the node E_(n) will be transferred undiminished through T₃ ' to the node O_(n-1).

At the third stage of the circuit in FIG. 1, since A_(n-2) has a binary zero value, ground potential will be applied to the gates of transistors T₂ " and T₃ ", maintaining these two devices in their off state. Correspondingly, since A_(n-2) has a binary one value, the positive potential V_(dd) will be applied to the gates of transistors T₁ " and T₄ " maintaining them on. Thus, the ground potential at the node E_(n-1) will be transferred undiminished to the node E_(n-2). And the positive potential V_(dd) minus V_(th) will be transferred undiminished to the node O_(n-2).

In the bottommost or fourth stage of the circuit of FIG. 1, since A₀ has a binary zero value, ground potential will be applied to the gates of transistors T₂ '" and T₃ "' maintaining them off. Correspondingly, since A₀ has a binary one value, the positive potential V_(dd) will be applied to the gates of transistors T₁ '" and T₄ '", maintaining these two devices in their on state. Thus, the ground potential at the node E_(n-2) will be transferred undiminished through the transistor T₁ '" to the E₀ node. And the positive potential V_(dd) minus V_(th) at the node O_(n-2) will be transferred undiminished through the transistor T₄ '" to the node O₀.

The positive potential at the node O₀ is applied to the gate of the depletion mode transistor T₆ and to the gate of the enhancement mode transistor T₇. The ground potential at the node E₀ is applied to the gate of the enhancement mode transistor T₅ and to the gate of the depletion mode transistor T₈. For the inverter T₅ and T₆, T₅ will be off and T₆ will be fully on and therefore the odd output will have a positive potential of +V_(dd) which is a binary one value. This can be interpreted as an indication that the four digit binary word input to the circuit has an odd parity. The inverter T₇ and T₈ will have the transistor T₇ on and the transistor T₈ almost off, thereby applying ground potential at the even output, corresponding to a binary zero. This can be interpreted as an indication that the parity of the four digit binary input word is not even.

It should be noted that the nodes O₀ and E₀ which are effectively the output terminals for the sequence of stages in the transmission logic parity circuit, are input to high impedance gates of the transistors T₅, T₆, T₇ and T₈. Thus it is seen that no DC current will flow through the successive stages of the parity circuit and therefore the circuit consumes virtually no DC power. The output stages consisting of the inverter T₅ and T₆ and the inverter T₇ and T₈ are static logic inverters and their depletion mode active loads T₆ and T₈, respectively, provide for full valued signal swings from ground potential to +V_(dd).

It is seen from FIG. 1 that the circuit topology for the transmission logic parity circuit is simple and its layout area is small when compared to prior art parity circuits. It should be appreciated that the circuit shown in FIG. 1 can either be an N channel FET circuit or a P channel FET circuit. In either case, the circuit is of a higher density than would be complementary MOSFET circuitry and yet the topology of the circuit shown in FIG. 1 achieves a low power dissipation, an advantage typically only available with CMOS circuits.

Although a specific embodiment of the invention has been disclosed, it will be understood by those of skill in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention. 

Having thus described our invention, what we claim as new, and desire to secure by Letters Patent is:
 1. A parity circuit for determining whether an odd or even number of binary bits having an even number of binary bits having a value of one, are present, at an n-bit plurality of binary operand bit inputs, comprising:n-stages of sequentially connected steering cells, each said cell including a true-value binary bit operand input and a complementary-value binary bit operand input for one said plurality of operand bit inputs, a first and a second indicating potential input terminals and a first and a second indicating potential output terminals; said first indicating potential input terminal of an i-th cell connected to said first indicating potential output terminal of the next preceding i+1th cell and said second indicating potential input terminal of said i-th cell connected to said second indicating potential output terminal of said next preceding i+1th cell; a first FET device in each said cell having its drain connected to said first indicating potential input terminal thereof, its source connected to said first indicating potential output terminal thereof, and its gate connected to said complementary-value binary bit operand input thereof; a second FET device in each said cell having its drain connected to said second indicating potential input terminal thereof, its source connected to said first indicating potential output terminal thereof, and its gate connected to said true-value binary bit operand input thereof; a third FET device in each said cell having its drain connected to said first indicating potential input terminal thereof, its source connected to said second indicating potential output terminal thereof, and its gate connected to said true-value binary bit operand input thereof; a fourth FET device in each said cell having its drain connected to said second indicating potential input terminal thereof, its source connected to said second indicating potential output terminal thereof, and its gate connected to said complementary-value binary bit operand input thereof; said first FET device in each of said cells forming a conductive path between said first indicating potential input terminal and said first indicating potential output terminal and said fourth FET device in the same cell forming a conductive path between said second indicating potential input terminal and said second indicating potential output terminal when said complementary-value binary bit operand input in the same cell is active; said third FET device in each of said cells forming a conductive path between said first indicating potential input terminal and said second indicating potential output terminal and said second FET device in the same cell forming a conductive path between said second indicating potential input terminal and said first indicating potential output terminal when said true-value binary bit operand input in the same cell is active; said first indicating potential input terminal in a first one of said cells in said sequence having a first DC potential continuously applied to it corresponding to a binary one bit value and said second indicating potential input terminal in said first one of said cells having a second DC potential continuously applied to it corresponding to a binary zero bit value said first DC potential being different from said second DC potential; said second indicating potential output terminal in a last one of said cells in said sequence outputting a signal corresponding to said first DC potential in response to an odd number of said cells having their respective true-value binary bit operand input active indicating an odd parity and said second indicating potential output terminal in said last cell outputting a signal corresponding to said second DC potential in response to an even number of said cells having their respective true-value binary bit operand input active indicating an even parity.
 2. The parity circuit of claim 1, which further comprises:a fifth FET device having its gate connected to the first indicating potential output terminal of said last one of said cells in said sequence, its drain connected to an odd output node and its source connected to said second potential; a sixth FET device having its gate connected to said second indicating potential output in said last one of said cells in said sequence, its drain connected to said first potential and its source connected to said odd output node; said odd output node having said first potential in response to an odd number of said cells having their respective true value binary bit operand input active indicating an odd parity.
 3. The parity circuit of claim 2, which further comprises:a seventh FET device having its gate connected to said second indicating potential output in said last one of said cells in said sequence, having its drain connected to an even output node and its source connected to said second potential; an eighth FET device having its gate connected to said first indicating potential output terminal in said last one of said cells in said sequence, its drain connected to said first potential and its source connected to said even output node; said even output node having said first potential in response to an even number of said cells having their respective true value binary bit operand input active indicating an even parity. 